The present invention relates to a process for producing a positive electrode for a non-aqueous electrolytic cell or battery in which manganese dioxide is employed as the active material for the positive electrode (cathode), a light metal such as lithium or sodium is employed as the active material for the negative electrode (anode), and an organic electrolytic substance is employed as the electrolyte.
It has been already proposed to employ manganese dioxide as the active material for the positive electrode in a non-aqueous electrolyte cell.
In general, since manganese dioxide contains a large amount of combined water in addition to adherent water, water contained in manganese dioxide tends to oxidize or otherwise adversely affects the active material for the negative electrode such as lithium if manganese dioxide is employed as the positive electrode of such a cell. Therefore, it has been proposed to heat-treat manganese dioxide at a temperature within the range of 250.degree.-350.degree. C., and further at a temperature range of 350.degree.-430.degree. C., in order to remove water contained in manganese dioxide.
On the other hand, in preparation of a positive electrode of a cell using manganese dioxide as the active material, it is a common practice to add a conducting agent such as carbon powder, since the conductivity of the manganese dioxide itself is low and a binder for increasing the binding force between the manganese dioxide powders and the powders of the conducting agent, these two agents being mixed together in the ambient atmosphere.
Thus, there arises a problem that manganese dioxide is combined or adhered with water again while it is mixed with the conducting agent and/or the binder in the ambient atmosphere even if use is made of manganese dioxide which has been heat-treated for removal of the contained water, thereby making it meaningless to heat-treat the manganese dioxide.
In order to solve this problem, a method has been proposed including the steps of heat-treating manganese dioxide at a temperature ranging from 350.degree. to 430.degree. C., adding a conducting agent and a binder to be mixed together followed by molding, and then heat-treating the thus molded body at a temperature of from 200.degree. to 350.degree. C. (see U.S. Pat. No. 4,133,856).
However, in this prior art method, manganese dioxide is firstly added with a conducting agent and a binder to be admixed together and molded, and the thus formed molded body is subjected to heat treatment, so that water confined in the molded body in the admixing step will not be completely removed by heating which is applied after the molding step. This presents another problem wherein the discharge property, and in turn the storage property of the product, are adversely affected. In addition, a further new problem arises in that since the molded body or article is surrounded and retained by a metal ring, the molded article is deflected by heating due to the difference in thermal expansion coefficients of the metal ring and the molded article. Furthermore, not only is a special heating space required for heating the molded articles since the finished molded articles are subjected to heating, but the heating process also becomes complicated to render the method unfit for application to mass production. Yet a further problem is that the molded article must be handled most carefully to prevent damage during the heating step since the molded article per se is thin and is retained only by the surrounding retention ring, resulting in difficulties in handling and mass production.